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Probably quite appropriately for the time of the year, there's been quite a few threads lately about proper choice of undergarments for cold weather. Having spent roughly half a century in a climate that some would consider unacceptably cold - while others just wonder what the big fuss is all "aboot", 'cause they're used to even colder climates than I am used to - I thought I'd like to chime in with some basic tips about how to avoid freezing your a$$ - or more probably, your fingers or toes - off while diving in cold water.
The text has become fairly long, but there's a summary at the bottom of the post, for those who don't care to read it all.
(And I'm deliberately putting this in the "Basic" forum, since it deals with basic principles of keeping warm
)
First, the disclaimers. Number one: "cold-ish" for me is below 10°C (sub-50F) water, while "cold" is below 5°C (sub-40F) water. And I don't like to dive when the air temp drops below -10°C (15F); breaking down the gear and getting out of the suit before everything has frozen solid is too much of a pain in the a$$ for me. Also, my regulator occasionally freeflows when it's that cold, and I don't like that. Number two: I have to confess I'm not an extremely experienced cold water diver. At the time of writing, I have between half a dozen and a dozen dives in cold water. However, I have more than three decades' worth of experience in dressing for the cold topside, including conditions like below -20°C and wind; or around freezing with gale and sleet. My subsequent ramblings are based on what I know about the physics and the physiology of losing body heat, with the addition of some personal experience, both underwater and topside.
Basic principles (physics and physiology)
The physics of heat loss should have been learned during school or during our OW theory sessions. So, we all should know that heat is lost through four phenomena:
By the way, radiation isn't a particularly significant factor for the temperature differences we're dealing with here. So, the concept of "space blankets" or "heat-reflecting socks" that are supposed to reflect body heat is just so much bovine manure. The "space blankets" could easily be replaced with a plastic tarp and work just as effectively, because they work by restricting convection, not by restricting radiation. The "heat reflecting socks" I've seen on TV shop and other just as reputable stores, with interwoven metal threads supposed to "reflect" your body heat is perhaps the worst. idea. evah. for keeping warm. As we (should) know, the heat loss through radiation is insignificant, while metal conducts heat even more freakin' effectively than water does...
More interesting than the physics is the physiology of freezing and the body's heat regulation strategies. The body is a wonderfully well-regulated system. If we get too warm, our bodies will increase circulation to the outermost parts of the body - the skin, the hands and the feet - to increase heat loss. If this isn't enough, we start to perspire, because the evaporation of sweat cools you very effectively. On the other hand, if we get too cold, our bodies will pull the blood towards the core, to decrease heat loss. If this isn't enough, we'll start shivering, because the extra muscle work will produce heat. If we get a bit on the cold side, our bodies will prioritize its most important bodyparts: first and foremost the brain, secondly the torso, while hands and feet are the first parts to be sacrificed if push comes to shove. And it will do so proactively. This is why your hands and feet often are the first bodyparts that will feel cold when you sit down for a break during your cold weather hike.
Applying the basic principles
So, how do we apply our knowledge of the physics and physiology of freezing to keep warm?
First, consider your neck and head. Choose a thick, warm hood with a good fit. Your brain is the most important organ you have, and your body will never restrict circulation to that bodypart. Which means that your head - and the neck with the arteries and veins carrying blood to and from the brain - are heat sinks of monumental proportions, compared to the size they take up (insert "big-headed" joke here). Topside, I like to say that a good cap makes up for at least one thick sweater. So, before buying a thicker set of undergarments, check your hood. Is it thick or thin? Does it fit snugly, or is it loose? If everything checks out OK, you can start considering to buy new undergarments. If not, get a good hood first.
The next to consider is your torso, and we'll start with the base layer/wicking layer. It's important to choose the right fiber here. Cotton is the worst, by a big margin, if you want to keep warm. Wet - or damp - cotton feels clammy and provides virtually no insulation. On the other hand, cotton is very effective in keeping that moisture close to your skin and not wicking it away.
At the other end of the scale, you find wool. Yes, wool. Forget your childhood experiences of itchy underwear, most modern wool undergarments are no-itch and can be worn by everyone except the most sensitive of us. Myself, I'll even accept a little itching since wool is the best fiber you can choose if you're planning on being a little damp. Wool's position relative to the other fibers is even better if it's wet: no other fiber can absorb 30% of its own weight in moisture and feel dry, and no other fiber provides residual insulation when it's soaking wet. If your dry suit is ever flooded or has a significant leak, you'll be grateful that you chose a wool base layer.
Between the two extremes - cotton and wool - you'll find the synthetic fibers. Synthetic fibers are often marketed as "technical" or somesuch. Some synthetics are a little bit better than average; some are a little bit worse. The good thing about synthetics is that they absorb very little moisture - some fibers none at all. Polypropylene is the best in this respect, and good polyesters aren't bad either. Just not as good as the polypro. Polypro is actually a pretty good base layer provided your heat production is high enough to drive the moisture from that base layer into your middle layer, and it's my personal choice if I'm cross-country skiing or bicycling (but not when jogging; I hate jogging!) at medium to high intensity levels, in temperatures down to around -10°C / 15F (below that, I reduce my intensity level and wear wool, because my bronchi don't like that I'm breathing hard when it's really cold. I always start coughing, especially after coming into the warmth again). The downsides of polypro are 1: after a year or two of regular use, it'll smell like ripe roadkill only minutes after you've put it on. Even if you wash it after every use. And 2: If you get a little bit cold and the garment is damp or wet, polypro provides poor insulation and isn't particularly comfortable. Just like the other synthetic fibers are when wet...
If you can get mesh underwear, that'll be even better than a regular garment, since the mesh traps air next to your skin while providing the minimum of damp fabric in contact with your skin. So break out the fishnet stockings, ladies! Or, to be more serious, look for something similar to the Aclima Woolnet in wool or the Brynje Super Thermo in polypro. If you want something thicker, the terrycloth-like garments like the ones made by Woolpower are a good alternative, I use those as well, although I almost always use my Woolnets underneath my Woolpowers.
During the last 10-15 years, undergarments combining polypro (or other "high-performance" "technical" synthetics) and wool have hit the market, at least here in Northern Europe. It seems like a good idea to combine the moisture-transporting properties of modern synthetics and the insulating properties of wool, but I have no personal experience with those combination garments. Personally, I prefer to decide by myself if I want to prioritize moisture transport (and use polypro next to my skin) or insulation properties when damp (and use wool next to my skin). YMMV, of course.
That was the base layer, next is the middle layer. As previously mentioned, the function of an undergarment is not to insulate, but to trap air which insulates. This means that if you're diving with an absolute minimum of weight and you're feeling a little shrink-wrapped at depth, your undergarment can't do its job properly. You need to give it some air it can trap. When it's cold, you can give it a little more air to trap by overweighting just a tiny bit, and then adding some more air to your drysuit than strictly necessary to avoid squeeze. In the summer, I dive about minimum weight and both my suit and my BCD are quite empty at the safety stop. In the winter, I use about 2kg more to weigh down the extra air I put into my suit to keep warm. If the water's really cold, I'm reverting to putting most of my buoyancy air into my suit, as I was taught - and did - during my first drysuit dives. Try it, it makes a huge difference! If your undergarment isn't warm enough, even after adding a little extra weight, try getting a piece of closed cell foam, like the type used as a cheap sleeping bag pad, and cover your belly and chest with it. You can keep it in place by sticking it under your drysuit suspenders, and it provides extra insulation where your air bubble is at its thinnest, on the bottom-facing side of your torso. But reckon on adding even a little more weight, because those plates are pretty buoyant, and they don't compress much under pressure since they're closed-cell.
Finally, let's look at your hands and feet. If you've dressed properly and you're using enough air in your drysuit, you may find that those gloves and socks you already have aren't that cold after all. That's because when you were on the cold side, your body restricted circulation to those least important and most expendable body parts. If they still are cold, the next step would be to check that your gloves and socks/boots aren't too tight. If you've stuffed so many pairs of thick socks into your drysuit boots that you can't wiggle your toes, take off a pair. Yes, take them off. If you constrict circulation to your hands and feet, they will be cold, no matter what you're wearing. Make sure that your feet are dry, that the socks wick moisture properly, and that your feet aren't squeezed into the boots. If all that checks out, your feet will most probably be warm enough. If they're not, it's time to break out the scissors, glue and tape to change your drysuit boots - or socks - for a larger pair to provide enough space for that precious insulating air. Of course, the type of fiber/fabric in your socks should be chosen the same way you choose the fiber of your torso base layer. My favorites are Woolpower's 400gsm logo socks, in wool terry, maybe with a pair of their 600 gsm socks outside if there's room for it. Or, alternatively, a pair of thin wool dress socks with the 600gsm socks outside if there isn't room for two pairs of terry socks.
Summary
To keep your hands and feet warm, you should:
To keep your core warm, you should:
Further discussions about preferred brands and preferred synthetic fibers are left to the audience. And I almost forgot: happy cold water diving!
The text has become fairly long, but there's a summary at the bottom of the post, for those who don't care to read it all.
(And I'm deliberately putting this in the "Basic" forum, since it deals with basic principles of keeping warm
)First, the disclaimers. Number one: "cold-ish" for me is below 10°C (sub-50F) water, while "cold" is below 5°C (sub-40F) water. And I don't like to dive when the air temp drops below -10°C (15F); breaking down the gear and getting out of the suit before everything has frozen solid is too much of a pain in the a$$ for me. Also, my regulator occasionally freeflows when it's that cold, and I don't like that. Number two: I have to confess I'm not an extremely experienced cold water diver. At the time of writing, I have between half a dozen and a dozen dives in cold water. However, I have more than three decades' worth of experience in dressing for the cold topside, including conditions like below -20°C and wind; or around freezing with gale and sleet. My subsequent ramblings are based on what I know about the physics and the physiology of losing body heat, with the addition of some personal experience, both underwater and topside.
Basic principles (physics and physiology)
The physics of heat loss should have been learned during school or during our OW theory sessions. So, we all should know that heat is lost through four phenomena:
- Conduction,
- Convection,
- Evaporation and
- Radiation
By the way, radiation isn't a particularly significant factor for the temperature differences we're dealing with here. So, the concept of "space blankets" or "heat-reflecting socks" that are supposed to reflect body heat is just so much bovine manure. The "space blankets" could easily be replaced with a plastic tarp and work just as effectively, because they work by restricting convection, not by restricting radiation. The "heat reflecting socks" I've seen on TV shop and other just as reputable stores, with interwoven metal threads supposed to "reflect" your body heat is perhaps the worst. idea. evah. for keeping warm. As we (should) know, the heat loss through radiation is insignificant, while metal conducts heat even more freakin' effectively than water does...
More interesting than the physics is the physiology of freezing and the body's heat regulation strategies. The body is a wonderfully well-regulated system. If we get too warm, our bodies will increase circulation to the outermost parts of the body - the skin, the hands and the feet - to increase heat loss. If this isn't enough, we start to perspire, because the evaporation of sweat cools you very effectively. On the other hand, if we get too cold, our bodies will pull the blood towards the core, to decrease heat loss. If this isn't enough, we'll start shivering, because the extra muscle work will produce heat. If we get a bit on the cold side, our bodies will prioritize its most important bodyparts: first and foremost the brain, secondly the torso, while hands and feet are the first parts to be sacrificed if push comes to shove. And it will do so proactively. This is why your hands and feet often are the first bodyparts that will feel cold when you sit down for a break during your cold weather hike.
Applying the basic principles
So, how do we apply our knowledge of the physics and physiology of freezing to keep warm?
First, consider your neck and head. Choose a thick, warm hood with a good fit. Your brain is the most important organ you have, and your body will never restrict circulation to that bodypart. Which means that your head - and the neck with the arteries and veins carrying blood to and from the brain - are heat sinks of monumental proportions, compared to the size they take up (insert "big-headed" joke here). Topside, I like to say that a good cap makes up for at least one thick sweater. So, before buying a thicker set of undergarments, check your hood. Is it thick or thin? Does it fit snugly, or is it loose? If everything checks out OK, you can start considering to buy new undergarments. If not, get a good hood first.
The next to consider is your torso, and we'll start with the base layer/wicking layer. It's important to choose the right fiber here. Cotton is the worst, by a big margin, if you want to keep warm. Wet - or damp - cotton feels clammy and provides virtually no insulation. On the other hand, cotton is very effective in keeping that moisture close to your skin and not wicking it away.
At the other end of the scale, you find wool. Yes, wool. Forget your childhood experiences of itchy underwear, most modern wool undergarments are no-itch and can be worn by everyone except the most sensitive of us. Myself, I'll even accept a little itching since wool is the best fiber you can choose if you're planning on being a little damp. Wool's position relative to the other fibers is even better if it's wet: no other fiber can absorb 30% of its own weight in moisture and feel dry, and no other fiber provides residual insulation when it's soaking wet. If your dry suit is ever flooded or has a significant leak, you'll be grateful that you chose a wool base layer.
Between the two extremes - cotton and wool - you'll find the synthetic fibers. Synthetic fibers are often marketed as "technical" or somesuch. Some synthetics are a little bit better than average; some are a little bit worse. The good thing about synthetics is that they absorb very little moisture - some fibers none at all. Polypropylene is the best in this respect, and good polyesters aren't bad either. Just not as good as the polypro. Polypro is actually a pretty good base layer provided your heat production is high enough to drive the moisture from that base layer into your middle layer, and it's my personal choice if I'm cross-country skiing or bicycling (but not when jogging; I hate jogging!) at medium to high intensity levels, in temperatures down to around -10°C / 15F (below that, I reduce my intensity level and wear wool, because my bronchi don't like that I'm breathing hard when it's really cold. I always start coughing, especially after coming into the warmth again). The downsides of polypro are 1: after a year or two of regular use, it'll smell like ripe roadkill only minutes after you've put it on. Even if you wash it after every use. And 2: If you get a little bit cold and the garment is damp or wet, polypro provides poor insulation and isn't particularly comfortable. Just like the other synthetic fibers are when wet...
If you can get mesh underwear, that'll be even better than a regular garment, since the mesh traps air next to your skin while providing the minimum of damp fabric in contact with your skin. So break out the fishnet stockings, ladies! Or, to be more serious, look for something similar to the Aclima Woolnet in wool or the Brynje Super Thermo in polypro. If you want something thicker, the terrycloth-like garments like the ones made by Woolpower are a good alternative, I use those as well, although I almost always use my Woolnets underneath my Woolpowers.
During the last 10-15 years, undergarments combining polypro (or other "high-performance" "technical" synthetics) and wool have hit the market, at least here in Northern Europe. It seems like a good idea to combine the moisture-transporting properties of modern synthetics and the insulating properties of wool, but I have no personal experience with those combination garments. Personally, I prefer to decide by myself if I want to prioritize moisture transport (and use polypro next to my skin) or insulation properties when damp (and use wool next to my skin). YMMV, of course.
That was the base layer, next is the middle layer. As previously mentioned, the function of an undergarment is not to insulate, but to trap air which insulates. This means that if you're diving with an absolute minimum of weight and you're feeling a little shrink-wrapped at depth, your undergarment can't do its job properly. You need to give it some air it can trap. When it's cold, you can give it a little more air to trap by overweighting just a tiny bit, and then adding some more air to your drysuit than strictly necessary to avoid squeeze. In the summer, I dive about minimum weight and both my suit and my BCD are quite empty at the safety stop. In the winter, I use about 2kg more to weigh down the extra air I put into my suit to keep warm. If the water's really cold, I'm reverting to putting most of my buoyancy air into my suit, as I was taught - and did - during my first drysuit dives. Try it, it makes a huge difference! If your undergarment isn't warm enough, even after adding a little extra weight, try getting a piece of closed cell foam, like the type used as a cheap sleeping bag pad, and cover your belly and chest with it. You can keep it in place by sticking it under your drysuit suspenders, and it provides extra insulation where your air bubble is at its thinnest, on the bottom-facing side of your torso. But reckon on adding even a little more weight, because those plates are pretty buoyant, and they don't compress much under pressure since they're closed-cell.
Finally, let's look at your hands and feet. If you've dressed properly and you're using enough air in your drysuit, you may find that those gloves and socks you already have aren't that cold after all. That's because when you were on the cold side, your body restricted circulation to those least important and most expendable body parts. If they still are cold, the next step would be to check that your gloves and socks/boots aren't too tight. If you've stuffed so many pairs of thick socks into your drysuit boots that you can't wiggle your toes, take off a pair. Yes, take them off. If you constrict circulation to your hands and feet, they will be cold, no matter what you're wearing. Make sure that your feet are dry, that the socks wick moisture properly, and that your feet aren't squeezed into the boots. If all that checks out, your feet will most probably be warm enough. If they're not, it's time to break out the scissors, glue and tape to change your drysuit boots - or socks - for a larger pair to provide enough space for that precious insulating air. Of course, the type of fiber/fabric in your socks should be chosen the same way you choose the fiber of your torso base layer. My favorites are Woolpower's 400gsm logo socks, in wool terry, maybe with a pair of their 600 gsm socks outside if there's room for it. Or, alternatively, a pair of thin wool dress socks with the 600gsm socks outside if there isn't room for two pairs of terry socks.
Summary
To keep your hands and feet warm, you should:
- Keep your core warm. If your core is just a little cold-ish, your hands and feet will be cold, no matter what you wear there.
- Make sure that blood flow to the feet isn't restricted in any way. Don't stuff your drysuit boots or socks so full of socks that you can't wiggle your toes a little bit.
- Use the same principles of dressing as for your core: Use a good wicking base layer, with as much middle layer as there's room for. But not more.
To keep your core warm, you should:
- Keep your head and neck warm by using a good hood. If your head and neck are poorly protected, you'll almost always be cold.
- Use a good wicking layer next to your skin. Wool is the best. Mesh is great. Especially if you get a significant leak in your suit or your seals.
- Always keep some air in your suit, preferably a little more than what's needed to avoid squeeze. If you need to add some weight to accommodate that air, add some weight. Not much, just a little.
Further discussions about preferred brands and preferred synthetic fibers are left to the audience. And I almost forgot: happy cold water diving!
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